Eating large amounts of fruit and vegetables can make you happier, Queensland research has found.

The University of Queensland study suggests eating eight or more portions of fruit and vegetables a day improves mental wellbeing as well as physical health.

Health economics researcher Dr Redzo Mujcic from UQ's school of pharmacy said the study involved more than 12,000 Australian adults.

"What I wanted to look at is whether it improves also our mental wellbeing or mental health as well as physical health," he told 612 ABC Brisbane.

Dr Mujcic said Australia's current guidelines on fruit and vegetable consumption had very little empirical evidence to back them up and were mostly concerned with physical health and longevity.

His study examined people's choices on fruit and vegies, and rated these against their levels of satisfaction, stress and vitality, and other mental health markers.

"It comes up the more you eat the better, but there's also some optimal points.

"Eating about five fruits and five vegetables [per day] makes us the happiest we can be in that case.

"This holds for a number of mental health measures and it sounds like a big number but it's actually consistent with recent evidence coming from the United Kingdom as well as New Zealand.

"This is based on a longitudinal household survey which takes place every year in Australia – it started in 2000 - it covers about 12,000 households or individuals."

Dr Mujcic said the effects were strongest among women, although he did not know why.

He said wellbeing levelled out among people who ate more than this amount, but that fewer than 10 per cent of those surveyed were eating the optimal 10 serves per day.

"The message coming out of this is if we can show a little bit more by using large-scale randomised control trials to actually get at the causal effect of this relationship, if mental health really is affected by the fruits and vegetables that we eat, the governmental policy makers need to do something about promoting larger amounts of consumption.

"The methods I employed are a lot richer than just observing people at one point in time because we observed them [over] multiple periods but still the causal effect is very difficult to get at."